A person is defined by his highest and complete aspect (just as a billionaire is not called a millionaire). Thus a person is his kesser. Kesser here is usually understood as rutzon. However in Lkm 24:7 Rabbainu NNNNM reveals that it is a hybrid of a. Misader and mi-yashev hasechel which is blessed from the hands of the world above him. And b. Emuna.
Mukom, space, G-d created to hold creation. Creation are creatures each defined by their kesser. A particular mukom is a reference to a particular kesser, and mukom in general is the container of all the kessers, it is the faculty of becheira - choice.
Creation is from the risheemu. By achieving yishuv hadaas, so that the misader and miyashev is set, this flips the switch of the becheira-place allowing the kav Ain Sof to shine the utter unity of HY.